The invention relates to a rotary-wing aircraft rotor whose blades are, at least for some of them, foldable and equipped with electrical equipment, for example a de-icing or anti-icing equipment, requiring the routing of electrical energy or signals between the blades and an electrical collector placed at the centre of the hub of the rotor. This routing of electrical energy or signals is provided by an electrical connection installation, essentially comprising an electrical harness comprising, for each blade, at least one electrical connecting cable, tied to a member for linking the corresponding blade to the hub of the rotor, and provided at its ends with connectors to ensure an electrical connection between the collector and the blade.
More precisely, the invention relates to a rotary-wing aircraft rotor, in particular a helicopter main rotor, of the type known in particular by EP-0 754 623 and FR 2 781 198 and comprising:
a hub, designed to be driven in rotation about an axis of the hub which is the axis of rotation of the rotor,
at least two blades, each of which is connected to the hub by a link member that is substantially radial with respect to the axis of rotation, and whose radially outer end is shaped like a fork in which the corresponding blade has its root held by two blade pins substantially parallel with each other and each one traversing aligned bores in the fork and the blade root, at least one blade being foldable on one side of the rotary wing aircraft and having at least one detachable blade pin, such that the withdrawal of the said detachable pin from the blade root and from the fork of the link member, after withdrawing at least a first detachable member for retaining the said detachable blade pin in the said fork, allows the pivoting of the blade about the other pin forming a blade pivot pin, and
an electrical connection installation comprising, for each blade, at least one electrical connecting cable connecting a first connector, carried by the hub and electrically connected, for example powered, on the latter, to a second connector on the blade and connected to at least one electrical equipment of the said blade, for example a de-icing or anti-icing equipment.
On a rotor according to EP 0 754 623, the connecting cable, for at least one manually foldable blade, comprises a first section, radially towards the outside, arranged like an overhead hook and extending from this blade to the corresponding link member, and connecting the second connector on this blade to a first end, in a radially outer position, of a second section of connecting cable, held substantially radially on this link member. This overhead hook of the connecting cable has a rounded cross section, possibly an armoured structure, and is connected to a plug of the second connector, this plug being connected to the socket of this second connector, this socket being fixed to the blade and connected to the icing or anti-icing equipment of that blade.
During the foldings of the blade, the pivotings of the blade in the radially outer fork of the corresponding link member can introduce damaging tensions in the overhead hook and in the second section of the connecting cable and in the second connector, and/or this overhead hook can oppose a complete folding of the blade.
In order to overcome this disadvantage, it is provided in EP 0 754 623 that the plug of the second connector, at the corresponding end of the overhead hook of the connecting cable, is connected in a detachable manner to the socket of the second connector, which is fixed on the blade. In fact, it is not recommended to give this overhead hook a length sufficient to allow the complete folding of the blade without disconnection at this connector, because an overhead hook of such length would have large forces applied to it and would be subjected to ample flutter movements, favouring its unwanted catching on adjacent components, such as blade root pendular anti-vibration devices, or drag dampers, on a rotor in rotation, on which the corresponding blade carries out angular deflections in pitch, flapping and drag.
Consequently, if it is desired to retain the advantages procured by the other characteristics of the connection installation described in EP 0 754 623, which can be referred to advantageously for more information, it is not possible to avoid manual disconnections and connections between the plug and the socket of the second connector in the case of manual folding or unfolding (or deployment) of the blades, before the folding and after the return of a blade to the flight configuration position respectively.
FR 2 781 198 proposes improvements to rotors with foldable blades and an electrical de-icing installation according to EP 0 754 623, in particular in order to reduce the stresses and/or movements of the connecting cable in its overhead hook section connecting the link member to the second connector on the blade, when the rotor is rotating and during the operations of folding and unfolding the blades.
For this purpose, according to FR 2 781 198, an elongated part of this overhead hook, of substantially flattened rectangular cross section, whose biggest dimension is oriented substantially parallel with the axis of rotation of the rotor, is held in a member, mounted in a fixed manner or pivoting about the folding spindle, in the substantially axial extension of this folding spindle, and arranged as a fork in which the said elongated part of flattened cross section is engaged and held by at least one elastic tab. This retaining fork prevents the displacements of the overhead hook on either side of the folding spindle, during a blade folding or unfolding, which prevents torsions harmful to this section of connecting cable, and it is no longer necessary to disconnect the link between the overhead hook and the de-icing equipment at the level of the second connector, before the folding of the blade, provided that the length of this overhead hook is sufficient without being so long that it generates the said disadvantages (flutter and unwanted catching).
But the flattened rectangular cross section of this overhead hook section of cable above the link between the blade root and the link member can generate a certain aerodynamic drag and cause a disturbing slipstream phenomenon. Furthermore, considering the angular movements, in particular of flapping of this section of cable and of its mechanical link with the link member, when that latter and the blade are carrying out these angular movements, it has proved necessary to form recesses in the periphery of a profiled dome covering the rotor head, and this amplifies the said slipstream phenomenon.
The basic problem for the invention is to overcome these disadvantages whilst avoiding the disconnection between the connecting cable and the second connector on the blade, for the folding of the latter, and avoiding the formation of a disturbing slipstream, caused by recesses in the profiled dome surmounting the rotor head and by a section of connecting cable with a flat profile oriented substantially parallel with the axis of the rotor.
For this purpose, the rotary wing aircraft rotor according to the invention, of the type described above, is characterized in that the connecting cable, for at least one foldable blade, comprises a first flexible section, of essentially cylindrical shape with rounded cross section, preferably substantially circular, connecting the said second connector to a first end, in a radially outer position, of a second section, held on the corresponding link member, of the said connecting cable, whose first section comprises a releasable part which, in the flight configuration of the blade, is maintained above the detachable blade pin by holding means tied to the said detachable blade pin, and also detachable to be able to be withdrawn before the folding of the blade, the said holding means being arranged in such a way as to allow a manual release of the releasable part before their withdrawal, such that the said releasable part is manually released from the said holding means before their withdrawal and such that the folding of the blade by pivoting about the said pivot pin causes the first section of cable to curve and move naturally in order to accommodate itself to the said folding without disconnection at the level of the second connector.
Advantageously, in a simple and practical embodiment, the holding means comprise a cradle formed in the upper end, protruding above the said fork, of a detachable cable holding pin, engaged in the said detachable blade pin, and held in the latter by at least a second detachable holding member, the said releasable part being held, in the flight configuration of the blade, in the said cradle by at least one detachable holding component, such that after the detachment of the said detachable holding component and the withdrawal of the said first and second detachable holding members, the releasable part of the said first section of cable can be released manually from the cradle, and the said detachable blade pin and cable holding pin can be withdrawn from the said fork and from the blade root, for the folding of the blade.
The rounded shape of the cross section of the first section of cable sets up only a limited aerodynamic drag and allows, at the level of the connection with the first end of the second section of cable, a fixing much closer to the link member, such that it is no longer necessary to form recesses in a protective dome of the rotor head. Furthermore, no matter on which side of the helicopter the folding of a blade is carried out, the first section of connecting cable is held, in the flight configuration of the blade, by its releasable part, and by the intermediary of the cradle and the cable holding pin, on that one of the two blade pins that does not constitute the pivot pin for the folding, such that after having manually released this section of cable from the cradle and withdrawn the cable holding pin and the detachable blade pin, this section of cable is completely free between the second connector, on the blade, and the first end of the second section of cable, on the link member, and can deform naturally, in particular it can curve, and move, in particular towards the blade pivot pin, such that it follows the blade during its folding without applying damaging tension to the second connector which it is not therefore useful to disconnect.
Advantageously, the cable holding pin is fitted in a detachable manner in the detachable blade pin, which is tubular, by engagement in the latter, substantially along the axis of the latter, and the said second detachable holding member comprises at least one spring pin, intended to traverse the said detachable blade pin transversely and to be engaged in at least one recess of the said cable holding pin in such a way as to hold the latter substantially axially in the detachable blade pin. Thus, if the recess on the cable holding pin is an orifice drilled through the latter, in such a way that the spring pin can simultaneously traverse transversely the detachable blade pin and the cable holding pin, the latter can be held axially and against any rotation in the detachable blade pin, whilst if the recess in the cable holding pin is a peripheral groove in this pin, the spring pin can hold this cable holding pin axially in the detachable blade pin whilst allowing its rotation about the axis of the latter, this rotation being able to favour the manual release of the releasable part of the first section of cable and/or the manual repositioning of this releasable part in the cradle.
In a known way, the first detachable holding member can also comprise at least one spring pin, intended to traverse the detachable blade pin transversely in its lower end protruding under the fork of the corresponding link member, in such a way as to lock the said detachable blade pin in the position of holding the blade root in the said fork, in the flight configuration of the corresponding blade, and it is then advantageous that this spring pin should constitute simultaneously the second detachable holding member intended to hold the cable holding pin in the detachable blade pin. Thus, if one or two spring pins is or are used to lock the detachable blade pin in the fork, in the flight configuration of the blade, this spring pin or these spring pins simultaneously hold the cable holding pin in the detachable blade pin. The withdrawal of this spring pin or these spring pins makes it possible to withdraw successively the cable holding pin from the detachable blade pin and then the detachable blade pin from the blade root and from the fork, or allows the simultaneous withdrawal of these two pins. But as a variant, the cable holding pin can be held axially in the detachable blade pin in such a way that the former is detachable only with the latter, these two pins being withdrawn or fitted simultaneously.
Advantageously, the releasable part of the first section of cable, which is intended to be held in a detachable manner in the said cradle, is delimited between two over-mouldings of excess thickness on the first section of cable in such a way as to lock the said releasable part in translation in the cradle.
In an advantageously simple embodiment, the detachable holding component can comprise at least one other detachable spring pin, intended to traverse the cradle transversely above the said releasable part of the first section of cable, in such a way as to hold the said releasable part in the cradle. But, as a variant, this detachable holding component can comprise at least one hook articulated on a side of the cradle and closable on the opposite side of the cradle, upon which the hook is intended to be fixed, preferably by at least one other detachable spring pin, in such a way as to hold the said releasable part in the cradle. It is easy to release manually the first section of cable from the cradle or to hold it in the latter by manipulating such detachable holding components.
Advantageously, for a better connection between the first and second sections of connecting cable, this second section extends over the corresponding link member, in a direction inclined with respect to the longitudinal axis of the said link member, and such that its first end, in a radially outer position, is offset laterally towards the outside and held on the said link member by a collar integral with a mount fixed on the link member, preferably by a spindle for holding one end of a drag damper in an attachment fork protruding laterally from the link member.
Also advantageously, as known from EP 0 754 623 and FR 2 781 198, and for the reasons given in these two documents, the second section of cable has an elongated part of substantially flattened rectangular cross section, maintained substantially flat on the top of the said link member, that is to say such that the largest dimension of its cross section is oriented substantially perpendicular to the axis of the rotor, in particular in order to facilitate the fixing of this second section of cable on the link member, to reduce the aerodynamic drag and to attenuate the mechanical forces applied to this section of cable.
Thus, the rotor according to the invention can also benefit from the advantages resulting from the use of other features of the electrical connection installation according to EP 0 754 623 and FR 2 781 198.
In particular, the second section of cable can be advantageously connected to the first connector on the hub by the intermediary of a third section of the connecting cable, the said third section comprising an overhead hook, in the shape of a flattened half-loop, of substantially flattened rectangular cross section whose largest dimension is substantially perpendicular to the axis of rotation, and whose concavity is facing substantially towards holding and articulation means connecting the corresponding link member to the hub, and substantially radially towards the axis of rotation, the said overhead hook being thus deformable in flexion and torsion in order to accommodate itself to the angular deflections in pitch, drag and flapping of the blade and its link member with respect to the hub, as known from the two documents mentioned above.
Similarly, the second section of cable can advantageously be connected to the overhead hook of the third section of cable by a joint connected to the link member by a link which is articulated at least in pivoting manner about an axis substantially parallel with or slightly inclined with respect to the longitudinal pitch change axis of the link member and of the blade, in order to attenuate the mechanical forces applied to the connecting cable whilst allowing a good take-up of the forces applied to the latter when the rotor rotates and the corresponding blade is carrying out its angular deflections in pitch, flapping and lag, as proposed in FR 2 781 198.